Add ability to set boot layout.

tools/gen-emoji.py

@@ -344,6 +344,21 @@ pub fn matches(emoji: Emoji, query: []const u8) bool {
     return true;
 }
 
+/// The table's own copy of `glyph`, or null if it isn't one of ours.
+///
+/// What comes back is static, so a caller can hold it for as long as it likes
+/// with nothing to free — which is what lets a glyph read out of a config file
+/// be handed to something that wants a pointer it can keep. A glyph the table
+/// doesn't have reads as no choice at all: the picker is where these come from,
+/// so anything else is a hand-edited file naming something this build can't
+/// draw at the size the row wants.
+pub fn lookup(glyph: []const u8) ?[:0]const u8 {
+    for (table) |entry| {
+        if (std.mem.eql(u8, entry.glyph, glyph)) return entry.glyph;
+    }
+    return null;
+}
+
 /// Every emoji the picker offers, in Unicode's order.
 pub const table = [_]Emoji{
 '''